POISONING AND TRAPPING = 291 
the phosphorus in carbon disulphide, after 
which the substance is mixed with any suitable 
material, as flour or meal or glucose in the rat 
and roach pastes (from 2 to 4 per cent. strong), 
or is formed into the waxy sticks offered for 
sale. Now its instability in contact with the 
oxygen of the air is so great that it is liable 
when dry, and has been known, to burst into 
flame, setting fire to everything it touched. 
Cases have occurred in the West where it has 
thus caused fires which destroyed entire fields 
of ripe wheat and barley, and buildings in which 
prepared phosphorus was stored. Some hazard 
attends the use even of carefully prepared phos- 
phorus pastes. 
Arsenic, in the form of Paris green or Lon- 
don purple is widely employed as an insecticide. 
It is comparatively cheap, but is by no’ means 
as deadly as phosphorus or strychnine. The 
smallest quantity known to have been fatal to 
a human being is 2.5 grains. Its action on ro- 
dents is exceedingly variable, and there is 
ample proof that rats after taking small doses 
frequently become entirely immune to its 
further effects. Moreover, it is likely to sour 
